# Trait core::iter::FromIterator 1.0.0 [−] [src]

    pub trait FromIterator<A>: Sized {
        fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> Self;
    }

Conversion from an `Iterator`.

By implementing `FromIterator` for a type, you define how it will be created from an iterator. This is common for types which describe a collection of some kind.

`FromIterator`'s `from_iter` is rarely called explicitly, and is instead used through `Iterator`'s `collect` method. See `collect`'s documentation for more examples.

See also: `IntoIterator`.

# Examples

Basic usage:

    use std::iter::FromIterator;

    let five_fives = std::iter::repeat(5).take(5);

    let v = Vec::from_iter(five_fives);

    assert_eq!(v, vec![5, 5, 5, 5, 5]);Run

Using `collect` to implicitly use `FromIterator`:

    let five_fives = std::iter::repeat(5).take(5);

    let v: Vec<i32> = five_fives.collect();

    assert_eq!(v, vec![5, 5, 5, 5, 5]);Run

Implementing `FromIterator` for your type:

    use std::iter::FromIterator;

    // A sample collection, that's just a wrapper over Vec<T>
    #[derive(Debug)]
    struct MyCollection(Vec<i32>);

    // Let's give it some methods so we can create one and add things
    // to it.
    impl MyCollection {
        fn new() -> MyCollection {
            MyCollection(Vec::new())
        }

        fn add(&mut self, elem: i32) {
            self.0.push(elem);
        }
    }

    // and we'll implement FromIterator
    impl FromIterator<i32> for MyCollection {
        fn from_iter<I: IntoIterator<Item=i32>>(iter: I) -> Self {
            let mut c = MyCollection::new();

            for i in iter {
                c.add(i);
            }

            c
        }
    }

    // Now we can make a new iterator...
    let iter = (0..5).into_iter();

    // ... and make a MyCollection out of it
    let c = MyCollection::from_iter(iter);

    assert_eq!(c.0, vec![0, 1, 2, 3, 4]);

    // collect works too!

    let iter = (0..5).into_iter();
    let c: MyCollection = iter.collect();

    assert_eq!(c.0, vec![0, 1, 2, 3, 4]);Run

## Required Methods

### `fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> Self`

Creates a value from an iterator.

See the module-level documentation for more.

# Examples

Basic usage:

    use std::iter::FromIterator;

    let five_fives = std::iter::repeat(5).take(5);

    let v = Vec::from_iter(five_fives);

    assert_eq!(v, vec![5, 5, 5, 5, 5]);Run

## Implementors

- [src]
  `impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V>`
- [src]
  `impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E>`

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